Two aspects of the immunology of Schistosoma mansoni infections will be studied: the nature of adult worm evasion of the immune response, and the nature of anti-adult worm immunity. The former will concentrate on the alpha 2-macroglobulin-like (alpha 2M-1) substance of the parasite. Its role as an immunogen or as an eclipsed antigen in infection will be examined by assaying for infection antibodies produced in baboons, as well as its ability to stimulate the lymphocytes of infected baboons to proliferate. Levels of circulating alpha 2M-1 in infected mice will be measured by radial immunodiffusion. Circulating complexes with antibody and alpha 2-M-1 will be sought with radiolabelled parasite antigen. Similar parasite antigens will be sought in the other major human schistosomes, and if found, their relationships to host alpha 2-macroglobulins will be ascertained by immunodiffusion and immunoabsorption techniques. Alpha 2-M-1's ability to inhibit lymphocytes in mitogen bastogenesis will be checked. The hypothesis of anti-oviposition immunity in infected primates will be tested, with special emphasis on the role of antibodies in inducing athrepsia. Correlation of anti-adult antibodies with fecundity immune criteria will be attempted. In vitro studies on antibody effects on worms, their egg-laying, and nutrient uptake will also be done. Identification of characteristics and specificities of tegument-bound antibodies will be attempted on eluted antibodies.